For molding nonconforming contours, which means undercuts in the mold it is common to work with loose parts. After the removal of the main part of the pattern, these are drawn into the created hollow space of the mold and then also removed, in order to be reassembled with the main part of the pattern. In the case of relatively narrow molds loose parts can not be used since the hollow space of the mold is not sufficiently wide. Here, separate cores have to be inserted in the produced mold.
Another possibility for molding nonconforming contours is offered by the technique according to which gasifiable models fill the mold. Hereby, the model within the mold is destroyed before or during casting. The application of this process is limited by the stability of the synthetic foam to be used which opposes relatively low resistance during the hardening of the molding material. This can lead to distortions and dimensional aberrations of the castings. For each casting a new model has to be made which then is completely gasified. Relatively large gas quantities have to be evacuated during the casting. The residues on the surface of the casting can deteriorate the quality of the casting.
Accordingly, it is the object of this invention to provide a process in which castings with nonconforming contours can be produced without the aforementioned disadvantages.